Central Performance Testing Research Articles

PSV-27 Serum Mineral and Vitamin Concentrations in Central Performance Tested Rambouillet Rams with and Without Angular Limb Deformities

Abstract Angular limb deformities (ALD) have historically affected 3 to 18% of Rambouillet ram lambs enrolled in central performance tests in the Northern great plains. Osteochondrosis, the underlying pathology of ALD, results in varying degrees of abnormal ossification in long bones and limits ram welfare and performance under extensive rangeland conditions. The objective of this research was to quantify serum mineral and 25-hydroxyvitamin D differences in rams with and without (non-affected) ALD. A total of 25 ram lambs (age = 189 ± 19 d; n = 13 ALD, n = 12 non-affected) were evaluated. Serum and body weight (BW) were collected on d 0, 28, 56, 83, and 112 of the test. Serum concentrations of 25-hydroxyvitamin D, macrominerals (Ca, Cl, K, Mg, Na, P, and S), and microminerals (Co, Cr, Cu, Fe, Mn, Mo, Se, and Zn) were quantified. Traits were analyzed as repeated measures with fixed effects of ALD status, sampling timepoint, and their interaction. An autoregressive type-I covariance structure with heterogenous variance was used to model the random ram effect. The ALD status x sampling timepoint interaction was significant (P ≤ 0.03) for serum 25-hydroxyvitamin D and Mg concentrations. Rams with ALD had greater 25-hydroxyvitamin D concentration at d 83 and 112 and greater Mg concentration at d 28 and 112 (P ≤ 0.05; Table 1). The main effect of ALD status was significant for serum Cl and greater for ALD than non-affected rams (3,672 ± 38.8 vs. 3,500 ± 38.3 mg/L; P < 0.001). Ram BW and serum concentration of all other minerals were similar between ALD and non-affected. Sampling timepoint affected several serum mineral concentrations as Ca generally increased with time, Co peaked at d 28, and Na decreased with time (P ≤ 0.03). Not surprisingly, BW also increased over time (P < 0.001). The range in serum mineral concentrations and percentage of rams deficient were: 25-hydroxyvitamin D (non-affected 32 to 241 mmol/L, 17%; ALD 35 to 160 mmol/L, 15%), Mg (non-affected 10.7 to 44.1 mg/L, 14%; ALD 11.7 to 45.0 mg/L, 14%), Cl (non-affected 3,066.3 to 4,024.5 mg/L, 21%; ALD 3,068.4 to 4,072.5 mg/L, 12%). While ALD and non-affected rams differed in key serum vitamin and mineral element concentrations, it’s a multifaceted disorder in which perinatal, endocrine, genetic, and nutritional conditions need to be researched to fully understand the etiology and mitigate its incidence.

Breeding Soundness Inspection and Production Features of Bullocks under Ecological Conditions in Free State Region, South Africa

Assessing the fertility of bullocks preceding to use as breeding animals make apparent economic if it were possible. Fertility is not possible predicted by means of a breeding soundness evaluation (BSE), but by the application of minimum standards to a set of accepted procedures, which supports informed decision makers to the breeding potential of the bullock. An bullocks found to satisfy these criteria in Central Performance Testing (CPT) known as Phase C, is reckoned to be breeding sound (BS). Furthermore, breeding success depends on the reproductive performance of both the cow and the bull. Breeding bull is likely to service a large number of heifers or cows in planned breeding season. The efficiency of a bullock can be based on the average daily gain (ADG) and feed conversion ratio (FCR) but poor breeding sound evaluation can be regarded as infertile. Bull breeding soundness evaluations (BSEs) are significant economic management of beef herd management and depends on adequate semen quality, physical soundness and serving capacity. Furthermore, assessment of scrotal circumference (SC), libido, testicular measurement and semen parameters often not done during a routine breeding soundness examination. The aim of this study was to depict using BSE whether bullocks would be fertile under Phase C. The relationship of BSE and production characteristics in central performance testing is challenging to identify fertility in bullocks within 112 given days of CPT. This study investigated performance data extracted from Integrated Registration and Genetic Information System (Intergis) managed by Agricultural Research Council Glen Bull Testing Centre. There were three breeds investigated, namely, Simmentaler, Santa Gertrudis and Limousin for the period of 2007 to 2017, were analysed to determine the dominance and importance of factors affecting breeding soundness classification.

PSXIV-18 Genetic improvement for resistance to gastrointestinal parasitism in growing meat goats and hair sheep through a centralized performance test in the southcentral USA

Abstract Progress from selecting meat goats and hair sheep from different farms in the southcentral United States for resistance to internal parasitism during three consecutive central performance tests was evaluated. Tests entailed 7–10 wk of data collection after artificial infection of growing males with Haemonchus contortus larvae. There were 44, 50, and 50 Boer, Kiko, and Spanish goats and 54, 55, 34, and 47 Dorper, Katahdin-farm-A, Katahdin-farm-B, and St. Croix sheep, respectively. In year 1, males were randomly selected and in years 2 and 3 were progeny of sires and females classified as highly and moderately resistant. Criteria for males was average daily gain and residual feed intake during the performance test and means of fecal egg count (FEC) and packed cell volume after artificial infection and for females was FEC and FAMACHA on-farm. There were interactions in FEC of breed×year (P < 0.001) for both species (1,046; 1,134; and 2,630 for Boer; 3,781; 1,239; and 1,216 for Kiko; 1,303; 1,357; and 1,464 for Spanish; 3,288; 1,956; and 1,315 for Dorper; 1,528; 1,759; and 2,241 for Katahdin-A, 2,414; 3,874; and 1,793 for Katahdin-B; and 1,371; 1,160; and 1,175 eggs/g for St. Croix in years 1, 2, and 3, respectively) and year×resistance group (RG; P = 0.005) for goats (1,359; 610, and 552 for high; 1,951; 1,268; and 1,440 for moderate; 2,821; 1,852; and 3,118 eggs/g for low RG in years 1, 2, and 3, respectively) but not for sheep (P = 0.639). In conclusion, resistance appeared greatest for Spanish and St. Croix within species and was increased by selection of Kiko and Dorper. For highly resistant goats, lower FEC in year 2 and 3 vs. 1, compared with no year differences for moderate and low RG, indicates selection progress, and the lack of similar differences for sheep may reflect their relatively greater resistance.

PSXIV-19 Heritability for growth and resistance to gastrointestinal parasitism in meat goats and hair sheep

Abstract Genetic selection for resistance to internal parasitism is of great research interest. Heritabilities were determined for average daily gain (ADG), logarithmic transformed fecal egg count (FEC), packed cell volume (PCV), and serum immunoglobin (Ig) levels of growing male meat goats and hair sheep from different farms in the southcentral USA during three consecutive central performance tests (CPT). Tests entailed 7–10 wk of data collection after artificial infection with Haemonchus contortus. In year 1, animals evaluated were selected randomly and in years 2 and 3 progeny of CPT sires classified as highly or moderately resistant, which included 46, 50, and 51 Boer, Kiko, and Spanish and 59, 61, 34, and 46 Dorper, Katahdin-farm A, Katahdin-farm B, and St. Croix, respectively. Females were classified accordingly on-farm based on FEC and FAMACHA. Pedigree records consisted of 32 and 57 known sires, 95 and 152 known dams including 4 and 10 full-sibs and 97 and 149 half-sibs for goats and sheep, respectively. Variance components and heritabilities were estimated by AIREML using WOMBAT with a multivariate animal model. Heritability estimates were 0.48 ± 0.214 and 0.85 ± 0.157 of ADG, 0.31 ± 0.237 and 0.20 ± 0.172 of FEC, 0.60 ± 0.206 and 0.24 ± 0.185 of PCV, 0.26 ± 0.172 and 0.51 ± 0.167 of IgA, 0.335 and 0.543 of IgM, and 0.14 ± 0.192 and 0.31 ± 0.190 of IgG for goats and sheep, respectively. Reasons for relatively high heritabilities for all traits include the low residual variance estimates due primarily to a standardized environment in the performance test. In conclusion, moderate to high heritabilities were found for growth performance and response to parasite infection for growing meat goat and hair sheep males under a standardized environment that suggests considerable for genetic improvement through selection.

PSXII-30 Genetic and phenotypic correlations for growth and resistance to gastrointestinal parasitism in meat goats and hair sheep

Abstract Genetic and phenotypic correlations for growth and response to parasite infection traits were estimated for growing male meat goats and hair sheep from different farms in the southcentral United States during three consecutive central performance tests (CPT). Data were collected for 7–10 wk after artificial infection with Haemonchus contortus, which included average daily gain (ADG), fecal egg count (FEC), packed cell volume (PCV), and immunoglobin (Ig) levels. Animals evaluated were selected randomly in year 1 and in years 2 and 3 progeny of CPT sires classified as highly or moderately resistant and included 46, 50, and 51 Boer, Kiko, and Spanish goats and 59, 61, 34, and 46 Dorper, Katahdin-farm A, Katahdin-farm B, and St. Croix sheep, respectively. Females were classified accordingly on-farm based on FEC and FAMACHA. Pedigree records included 4 and 10 full-sibs and 97 and 149 half-sibs for goats and sheep, respectively. Variance components and correlations were estimated by AIREML using WOMBAT with a multivariate animal model. The additive genetic correlation between FEC and PCV was negative for goats (r=-041, P < 0.001) but positive for sheep (r=0.21, P = 0.004), whereas the phenotypic correlation between FEC and PCV was nonsignificant for goats but negative for sheep (r=-0.252, P < 0.001). The genetic correlation between FEC and IgA was positive (r=0.39, P < 0.001) for goats but nonsignificant (P = 0.439) for sheep, whereas those of FEC with IgM and IgG were both negative (r=-0.369 and -0.732 with IgM and r=-0.284 and -0.702 for goats and sheep, respectively; P < 0.001). Genetic and phenotypic correlations between ADG and FEC were nonsignificant for both species. In conclusion, different relationships of FEC and PCV between species require careful attention during selection and the lack of relationship between ADG and FEC suggests that selection of growing male meat goats and hair sheep for resistance to internal parasitism will not adversely affect growth performance.

Genetic Selection for Resistance to Gastrointestinal Parasitism in Meat Goats and Hair Sheep through a Performance Test with Artificial Infection of Haemonchus contortus.

Simple SummaryInternal parasitism has been an important constraint to small ruminant production and anthelmintic resistance has become a worldwide issue. This study evaluated a 3-year genetic selection program through activities on-farm and a centralized performance test and also provided estimates of genetic parameters of growth and response to artificial infection with Haemonchus contortus by goats and sheep in the southcentral USA. Considerable species as well as breed differences were found in average daily gain and response to parasite infection. Average daily gain was greater for Boer than for Kiko and Spanish goats and slightly greater for Dorper than for St. Croix sheep. Infection level (number of eggs found in feces) of Spanish and St. Croix were relatively low each year, whereas that of Kiko and Dorper was lower after selection. An indicator of anemia (packed cell volume) did not always reflect infection level, which is probably reflective of differences among animals in resilience and susceptibility to haemonchosis. Moderate to high heritabilities were found for growth performance and response to parasite infection for growing meat goat and hair sheep males under a standardized environment that suggests considerable potential for genetic improvement through selection.Internal parasitism has been the leading cause of morbidity and mortality in small ruminants in many areas such as the southcentral USA. Among the different approaches and management practices to cope with internal parasitism, genetic selection for internal parasite resistance is recognized as one with considerable potential long-term impact. A central performance test with artificial infection of Haemonchus contortus for selection of growing meat goats and hair sheep for breeding to increase resistance to internal parasitism and on-farm selection of females was conducted for 3 years. The results varied considerably among breeds of goats and flocks of sheep. Spanish goats and St. Croix sheep maintained relatively low fecal egg count (FEC) each year, whereas for goats categorized as being of high resistance and Dorper sheep FEC decreased with advancing year. Packed call volume (PCV) and total serum immunoglobulin (Ig) levels were not strongly related to FEC. Genetic parameters varied between the two species, which might be related to previous selection pressure exerted for parasite resistance. Heritability of FEC was higher in goats than sheep. The genetic correlation between FEC and IgM and IgG was negative for both species, which suggests possible genetic association. Genetic and phenotypic correlations between ADG and FEC were nonsignificant for both species. In conclusion, different relationships of FEC and PCV between species require careful attention during selection and the lack of relationship between ADG and FEC suggests that selection of growing male meat goats and hair sheep for resistance to internal parasitism will not adversely affect growth performance.

Across and within breed differences in the relationship between packed cell volume and fecal egg count in growing meat goat and hair sheep males naturally and artificially infected with gastrointestinal nematodes.

The relationship between packed cell volume (PCV) and fecal egg count (FEC) in different breeds of meat goats and hair sheep infected with gastrointestinal nematodes, including Haemonchus contortus, was characterized. Growing males from eight commercial and two research farms (one Kiko, Spanish, Dorper, and St. Croix; three Boer; four Katahdin) in the southcentral United States were evaluated in a central performance test with ad libitum intake of a 50% concentrate pelleted diet. There were 84 Boer, 55 Kiko, and 57 Spanish goats and 52 Dorper, 129 Katahdin, and 49 St. Croix sheep. During adaptation, animals were dewormed then dosed with 10,000 infective H. contortus larvae. PCV and FEC were determined before deworming (i.e., natural infection potentially with multiple internal parasites) and 21, 28, 35, 42, and 49 days after artificial infection. Effects of species, breed, and year were analyzed with mixed effects models including day of sampling post dosing as a repeated measure and FEC and FEC × breed as covariates. Moreover, differences in correlation coefficients between PCV and logarithmic FEC (lnFEC) among species, breed, year, and day of sampling were evaluated. Breed affected (P ≤ 0.001) PCV in goats (24.8, 27.2, and 26.0% for Boer, Kiko, and Spanish, respectively; SEM = 0.42) and sheep (29.8, 26.7, and 31.0% for Dorper, Katahdin, and St. Croix, respectively; SEM = 0.28). There were effects of FEC × breed (P ≤ 0.029) on PCV for Boer, Kiko, Dorper, Katahdin, and St. Croix (-0.31, -0.33, -0.46, -0.46, and - 0.49% per 1000 eggs, respectively) but not for Spanish goats (P = 0.451). With all data, PCV and lnFEC with natural infection were highly correlated (P < 0.001) for Boer and Kiko goats and Dorper and Katahdin sheep (r = -0.59, -0.67, -0.77, and - 0.84, respectively) but not for Spanish goats or St. Croix sheep (P ≥ 0.323). Correlation coefficients for artificial infection with H. contortus were significant (P ≤ 0.002) except for Spanish goats, although values were lower (-0.40, -0.21, -0.23, -0.47, and - 0.28 for Boer, Kiko, Dorper, Katahdin, and St. Croix, respectively) compared with natural infection. In conclusion, PCV was not related to FEC in Spanish goats infected either naturally or artificially, and the nature of the relationship varied among breeds of goats and sheep. Based on the magnitude of the FEC × breed coefficient, sheep incurred a relatively greater reduction in PCV as FEC increased, and correlation coefficients indicate stronger relationships with natural than artificial infection.

1705 The response to artificial infection with Haemonchus contortus and growth performance of sheep and goat progeny of selected parents in a central performance test

1705 The response to artificial infection with Haemonchus contortus and growth performance of sheep and goat progeny of selected parents in a central performance test

Genetic parameters for type classification of Nelore cattle on central performance tests at pasture in Brazil

The objective of this study was to characterize Nelore cattle on central performance tests in pasture, ranked by the visual classification method EPMURAS (structure, precocity, muscle, navel, breed, posture, and sexual characteristics), and to estimate genetic and phenotypic correlations between these parameters, including visual as well as production traits (initial and final weight on test, weight gain, and weight corrected for 550 days). The information used in the study was obtained on 21,032 Nelore bulls which were participants in the central performance test at pasture of the Brazilian Association for Zebu Breeders (ABCZ). Heritabilities obtained were from 0.19 to 0.50. Phenotypic correlations were positive from 0.70 to 0.97 between the weight traits, from 0.65 to 0.74 between visual characteristics, and from 0.29 to 0.47 between visual characteristics and weight traits. The genetic correlations were positive ranging from 0.80 to 0.98 between the characteristics of structure, precocity and musculature, from 0.13 to 0.64 between the growth characteristics, and from 0.41 to 0.97 between visual scores and weight gains. Heritability and genetic correlations indicate that the use of visual scores, along with the selection for growth characteristics, can bring positive results in selection of beef cattle for rearing on pasture.

Optimum duration of performance testing for growth rate, feed intake, and feed efficiency in growing Boer bucks

Central performance testing of meat goats has increased in popularity recently, but minimum test duration has not been ascertained to assess accurately performance traits. This study was conducted to determine the minimum length of time required for accurate evaluation of growing Boer bucks for ADG, dry matter intake (DMI), DMI/BW0.75, and feed efficiency as assessed by ADG:feed intake and residual feed intake. Data were collected from 425 bucks enrolled in Langston University tests lasting 84 days from 2000 to 2009. Bucks averaged 111±25 days of age and 27±8kg BW at the beginning of the test, consumed a pelletized 50% concentrate diet ad libitum, and were weighed weekly. Daily feed intake was determined with Calan gates (American Calan, Inc., Northwood, NH) or automated MK3 FIRE feeders (Feed Intake Recording Equipment, Osborne Industries Inc., Osborne, KS). Weekly data of five performance traits were analyzed using the MIXED procedure of SAS with a repeated-measures model. Residual variance relative to that at 84 days (%) for the goats fed with Calan gates was 358, 293, 235, 193, 153, 127, 116, and 107% for ADG, 184, 173, 161, 149, 136, 123, 113, and 106% for DMI, 374, 317, 256, 203, 161, 137, 118, and 107% for DMI/BW0.75, 445, 320, 225, 162, 135, 124, 111, and 105% for ADG:feed intake, and 174, 154, 143, 128, 113, 107, 103, and 102% for residual feed intake at 28, 35, 42, 49, 56, 63, 70, and 77d, respectively. Residual variance relative to that at 84 days (%) for the goats fed with FIRE was 286, 221, 192, 174, 154, 134, 125, and 110% for ADG, 111, 113, 111, 112, 111, 107, 106, and 105% for DMI, 176, 155, 144, 130, 120, 110, 110, and 110% for DMI/BW0.75, 373, 258, 216, 171, 134, 119, 114, and 106% for ADG:feed intake, and 114, 101, 103, 95, 94, 92, 98, and 103% for residual feed intake at 28, 35, 42, 49, 56, 63, 70, and 77d, respectively. Under either Calan gates or FIRE feeding conditions, the duration of Boer buck performance tests could be decreased from the standard 84 to 63 days with little loss in accuracy.

Estimates of genetic parameters for traits measured in Phase A, C and D of the South African performance testing scheme

Numerous growth, reproduction, feed efficiency and shoulder measurement traits are recorded on beef cattle under the auspices of the South African Beef Cattle Performance Testing Scheme (NBCPTS). Best Linear Unbiased Prediction (BLUP) was first introduced to the South African beef industry on a national level in 1994, when univariate animal models were used to predict breeding values for traits measured in Phase A (birth and weaning weight) and B (yearling and 18 month weight) of the Scheme (Van der Westhuizen et al., 1995). In 1996 traits recorded in Phase D (growth tests on-farm) were also included into the analyses. Traits evaluated in Phase D include Average Daily Gain (ADGD), Kleiber Ratio (KR), Scrotum Circumference (SCD) and Shoulder Height (SHD). Although an univariate analysis uses all available pedigree information to calculate EBVs, it does not account for selection between traits, nor does it use the association (correlations) between traits to increase the accuracy of the EBVs. A common management practice in South Africa is to cull poor performing and functionally inefficient animals at weaning before further testing in Phase D, or alternatively, animals with above averageperformance are sent to central performance testing stations (Phase C). There is thus a high level of selection at this stage which should be accounted for in the national genetic evaluation. Traits measured in Phase C tests include Average Daily Gain (ADGC), Food Conversion Ratio (FCRC), Scrotum Circumference (SCC) and Shoulder Height (SHC). The objective of this study was to estimate covariance components between weaning weight and traits measured in Phase C and D of the NBCPTS. Results from this study will allow Phase C data to be included into the routine genetic evaluations, will account for the selection that occurs at weaning when analysing Phase C and D data, and will also increase the accuracy of EBVs by using the correlations between traits.

Genetic selection in farmed deer

Selection is the major tool used by breeders to improve the genetic quality of their livestock. Traditional methods of selection are well proven and useful in improving the economic merit of livestock. The performance of an animal is affected by its genetic quality and by the environment in which it is reared. While environmental improvement is expensive and requires continuous inputs, genetic improvement is cumulative and permanent, provided that selection is maintained. To select an animal on its genetic merit account must be taken of the environmental effects on its performance. Comparisons between the performance of animals on different farms or in different years are not valid unless they have genetic material in common. The speed at which genetic improvement is passed on to the rest of a population is affected by the variation and heritability of the traits being selected, the selection intensity and the generation interval. The deer population in the United Kingdom has a high degree of variation for important traits but the selection intensity is low and the generation intervals are larger than in other farmed species. Central performance testing, group breeding schemes and the use of artificial insemination are tools which will be important in the genetic improvement of farmed deer.

Many-sided performance testing of Finnsheep rams

Central performance testing of young rams has been conducted in Finland since 1975, in 1985—87 indoors as combined phenotype and 1/2-sib tests, which are the subject of this study. There were 100 individual boxes available, of which ca. 90 were annually used for Finnsheep (F). The rams were fed on concentrate diet (13.5 % DCP) ad lib. + hay. The test period was from 60 to 150 days of age. Feed intake (FI) was recorded daily, live weights (LW) fortnightly. At the end, MLD-areas were ultrasonically scanned, fleeces weighed, some linear body measurements taken, and fleshiness and wool quality scored. A total of 276 F rams were tested. They were progeny of 85 sires (2—4 half-brothers/sire). The means for all rams (30 selected rams) were: birth type 3.19 (3.18), rearing type 2.93 (3.01), age at start 64.3 (63.7) days, 60-day LW 19.5 (19.5) kg, 150-day LW 45.1 (47.6) kg, ADG 284 (312) g/d, FI 1.28 (1.34) kg/d, FE 4.49 (4.29) kg/kg gain, MLD-area 8.83 (9.63) cm2. There was considerable variation in the important traits (ADG, FI, FE, MLD-area), in spite of preselection. The phenotypic correlations of ADG with 150-d. LW, FI, Fl/kg gain and MLD-area were .61, .57, —.63 and .37, resp. (PC.001). Those of 150-d.LW with the last three traits were .59, —.15 NS and 0.44, resp.(P&lt; .001). Selection for ADG, 150-d. LW, Fl/kg gain and MLD area in the performance test appeared to improve the value of offspring for meat production in F.

A study on the reduction of age of boars at the entry into central performance test stations

A study on the reduction of age of boars at the entry into central performance test stations

Environmental effects on bull performance test results

ABSTRACTMeasurements of growth rate, food intake and food conversion efficiency on 235 Hereford bulls, from the first 4 years of a selection experiment, were used to assess the effects of rearing method, dam age and year/season of birth. Bulls were either reared artificially from birth to 84 days of age, or reared on their own dam to 84 or 168 days of age, to examine whether non-genetic effects on performance could be reduced by early weaning. All bulls were performance tested on ad libitum feeding from 200 to 400 days of age. Artificially-reared bulls had lower live weights at the start of test, which led to higher food conversion efficiency on test. Bulls reared naturally to 84 days of age were least affected by dam age and year/season of birth and performed as well as those weaned at 168 days of age. Earlier weaning of bulls entering central performance tests would reduce these environmental effects on performance, and may increase the accuracy of identifying bulls with genetically-superior growth and efficiency.

Relationship between central performance test for growth in Hereford bulls and growth and carcass traits of progeny

ABSTRACTFour central performance tests of growth in Hereford bulls from about 10 to 19 months of age on pasture were conducted in New Zealand. From the 100 bulls performance tested 63 were representatively sampled, including bulls with high and low performance test rankings, and progeny tested in dairy herds. Crossbred progeny were purchased from the dairy herds at 3 to 4 months of age, assembled in one location and reared together on pasture for 14 to 15 months prior to slaughter. Regressions of progeny growth and carcass traits on a number of different performance traits for growth of their sires were in almost all cases not statistically significant. The effective heritability, from offspring-sire regression, was 0·07 (s.e. 0·05) for final live weight and 009 (s.e. 0·06) for post weaning gain from about 200 to 550 days of age. It is concluded that central performance tests, as presently conducted in New Zealand, are of limited value for ranking breeding values of bulls for growth. Possible reasons for these results are discussed. It is suggested that pre-test environmental effects and age at the start of the central test are critical factors.

A review of central performance testing of beef bulls and of recent research in New Zealand

Recent information relevant to central performance testing for growth of beef bulls in New Zealand has been reviewed. Research shows that the influence of the calf's environment prior to 3–4 months of age has lasting effects on performance. Central performance tests as currently organised, starting with bulls from 6 to 10 months of age, are thus of limited value in New Zealand to indicate genetic superiority for traits such as growth rate.